Following on a previous post mentioning David Grann's "The Lost City of Z," here is some (very old) footage of Theodore Roosevelt, a few years after his presidency, looking for thrills by joining an expedition to map the source of the River of Doubt, in the Amazon rain forest.
Roosevelt went in 1913-14, but much of the footage of the actual river was taken in 1927, by George Dyott, another American explorer who followed the same route.